在dart中将变量指定为某种枚举

mbskvtky 于 2022-12-06 发布在其他

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Here's a little fun class:

abstract class Concept {
  late Enum option;
  String get name => option.name;
}

and you might implement it like this:

enum FeeOption {
  fast,
  standard,
  slow,
}
class FastFeeRate extends Concept {
  FeeOption option = FeeOption.fast;
}
print(FastFeeRate().name); // 'fast'

but then you get an error:

FastFeeRate.option=' ('void Function(FeeOption)') isn't a valid override of 'Concept.option=' ('void Function(Enum)').

So, how do you specify a variable as any kind of enum, not Enum itself?

dart

来源：https://stackoverflow.com/questions/74552397/specify-variable-as-some-kind-of-enum-in-dart

1条答案

按热度按时间

ddrv8njm1#

Your class Concept has a mutable ( late , but that doesn't matter) field with type Enum . That means it has a setter named option= with an argument type of Enum .
The subclass FastFeeRate is a subclass. It has another field (your class has two fields!) also named option , which has a setter with an argument type of FastFeeRate .
That's not a valid override. The subclass setter must accept all arguments that the superclass setter does, but it doesn't accept all Enum values.
What you might have intended to do is:

abstract class Concept<T extends Enum> {
  T option;
  Concept(this.option);
  String get name => option.name;
}
class FastFeeRate extends Concept<FeeOption> {
  FastFeeRate() : super(FeeOption.fast);
}

or

abstract class Concept<T extends Enum> {
  abstract T option;
  String get name => option.name;
}
class FastFeeRate extends Concept<FeeOption> {
  FastFeeRate option = FeeOption.fast;
}

depending on whether you want to define the field in the superclass or the subclass (but make sure to only define a concrete field in one of them).

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在dart中将变量指定为某种枚举

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